Coated paperboard and method of makign same



y 1950 H. c. FISHER ETAL 2,515,340

COATED PAPERBOARD AND METHOD OF MAKING SAME Filed April 1, 1947 IN VEN TORS. HdARY CZ I is/i 4mm raze Patented July 18, 1950 COATED PAPERBOARD AND METHOD OF MAKING SAME Harry 0. Fisher, Cincinnati, and Brainard E. Ohio, assignors to The Gardner Board and Carton 00., a corporation Sooy, Middletown,

of Ohio Application April 1, 1947, Serial No. 738,722

18 Claims.

Our invention relates to the formation of coated paper and paperboard which is resistant to wet rubbing and to the coloring of coated paper and paper board in various selected colors, more particularly but not necessarily when the board is given its mineral coat by an imprinting operation as a continuous step with the formation of the paper or board initially.

The invention herein is an adjunct to the modern practice of coating paper and paperboard webs, in which the coating is imprinted in a thin, relatively dry film on the traveling web as distinguished from being fiowed onto the web and smoothed with brushes and rolls. In such imprinting coating practices a film of a thickness of only two or three thousandths of an inch or so is established on a roll and by this roll applied to the traveling web. The roll may be one which receives a uniform film from gate rolls and distributing rolls or the coating may be applied to the imprinting roll by means of an intaglio roll in such fashion that a controlled and uniform film of coating is supplied to the imprinting roll. Also it has been suggested to control the roll film by means of doctors applied to the roll.

The coatings under such circumstances are considerably lower in water content than the normal coatings, and as exemplary thereof in the present case the coatings may be clay in an aqueous vehicle with proper binder of adhesive materials (and pigments when required), incor porated together, with the aqueous vehicle constituting around 45% of the coating. Such practices have the very great advantage that they can be applied as a part of a continuous process of web formation.

In application for Letters Patent Ser. No. 501,320, filed September 4, 1943, now Patent 2,419,207, issued April 22, 1947, is set forth a practice wherein a sizing material in an aqueous vehicle is applied to a traveling web of paper material on the breaker stack of calenders preceding the imprinting coating, wherein the effect of the calenders is plastically to smooth the treated surface ofthe traveling web and then while the said surface is still moist, the imprinting operation is applied. The advantage of this operation is that it gives a very much enhanced surface in the final calendered imprinted coated web, eliminating the defects incident to so'thin and dry a coating.

Such a clay coated web as results from this last noted practice, which has been found to be quite desirable where paperboard of ordinary composition is being used and the adhesive of the clay coating mixture is starch or equivalent nonwater resistant substance, has the limitation that the coating is not resistant to wet rubbing. It remains when finished not sufliciently resistant to water to permit of its use in the lithographic process of printing, using blankets which are wet with water, or where the operators hands are moist, or a moist sheet must be handled, moved about for drying, etc. In the absence of such a pretreatment, the same condition of lack of water resistance exists.

It has been known that with ordinary clay coatings used in highly aqueous condition and flowed onto a web followed by brushing and smoothing operations, it is possible to make the starch adhesive and the coating waterproof by means of certain substances. Chief among them is ureaformaldehyde resin along with its necessary acidic or other catalyst. Urea-formaldehyde resin, when in the early stages or hydrophilic stages of condensation, is soluble in water along with the starch adhesive in a normal coating, and under the influence of heat and time and in the presence of acid conditions such as, for example, in the presence of ammonium chloride which is also water soluble, will insolubilize the starch. Melamine aldehyde resin also has the property of waterproofing starch, acting in a like manner.

These and possibly other resins can be classed as relatively dry character and quite thin, the coat- 7 ing becomes gummy and dry on the imprinting roll and cannot be handled so as to result in a smooth final product, whether the former invention of application for patent above referred to is used or not.

We have found, however, by way of example, that if the resin substance be applied on the breaker stack of calenders, together or separately from the application of the inert, plastically smoothable surface treating agent, and in connection with catalyst, as hereinafter described, and while moist the web is then imprinted with the coating of the type heretofore noted, that with the use of proper heat in the following drying stage, and best also with proper heat during a storage period after final calendering, that for some reason not fully known, the waterproofing agent penetrates the imprinted coating and serves to render it water-resistant sumciently at least for easy use in the lithographic process of printing or other printing in the presence of moisture. We have also used this finding in that facet of our invention which relates to the coloring of coated paper and paperboard.

Customary methods for making colored coating for board vary to some extent. Thus in making the initial mix of mineral matter and binder, some or all of the usual white mineral such as china clay .is initially substituted for by other mineral pigments, lakes, toners, etc. Also there has been a practice of dyeing or pigmenting the solution of binder used, mixing it in with the white mineral mixture. Of course, also, the three types of ingredients, white mineral, color and colorless adhesive solution may be added during a mixing process while building up a batch.

Thereupon the finished colored mineral coating mixture is pumped through the coating applying .equipment, with the result that it becomes fouled with the particular color and must be cleaned completely before another color can be used on a subsequent order.

An essential object of our present improvement is to locate the point where the mineral coating mixture is colored as close to the point of application of the final coating to the board as possible. This eliminates the necessity of cleaning out anything but the coating applicator, the mixing point where the color is added and the connection between them.

General objects of our invention are the provision of improved coated paper and paper board, colored and'uncolored, and improved processes of making them.

,which an imprinted coating of regular white mineral was applied promptly. The result was that coloring matter penetrated into and permeated the imprinted coating, incident to the pressure type of operation involved and the necessary thinness of such imprinted coatings.

An alternative which suggests itself is to make a quick mix of coloring matter with a white mineral coating mixture just before application of the coating to the web. To do this one must select coloring matter which, if not water soluble, must be rapidly water-dispersible. There is no opportunity to make a colored mineral coating mixture quickly formed, with an otherwise finished clay coating mixture, if it takes time to grind in and disperse the coloring agents. However, water soluble or water dispersible colors will bleed if contacted with moisture and come off on the hands or any object which touches the unprotected colored coating.

As above indicated, and as will shortly be more fully explained, we have discovered a practical way to obtain a coated paper, the mineral matter of the coating being applied in a starch binder, which is in aqueous solution, but in which the starch of the binder becomes insolubilized subsequent to its imposition on the board or paper web.

Applicants have carried these improvements in the manufacture of uncolored, coated paper further and have discovered that they can use their process for forming a colored insolubilized starch bound mineral coat, using either a water-soluble dyestuif or a coloring matter not water-soluble although water-dispersible, e. g., a water-dispersible pigment. With water-soluble dyestufl the insolubilizing of the starch in the manner above referred to also fixes the dyestufl? so that a non-bleeding, non-smudging coating is produced by use of a soluble dye. With the coloring matter not water-soluble, although initially dispersible in water, the insolubilizing of the starch binds the insoluble but water-dispersible pigment into the coating on the board again to produce a non -bleeding, non-smudging coating.

Moreover the advantages are realized of the practice of introducing the coloring matter into a mineral coating by a mixing operation right at the coating machine, saving the fouling up of equipment and minimizing the cleaning of all the mixing equipment incident to change of colors. Our invention applies also when this advantage is foregone and the coloring is applied to the coating during its initial formation as in regular practice.

In the drawing, we have shown a diagram of a piece of apparatus which may be placed at the end of the driers of a board machine. The rolls I are the final drier rolls, and the web 2 passes around the stack of breaker calender rolls 3. There are water boxes 4 (so-called) which are used to flow material onto the web as it passes around the calender rolls 3. From the calender stack the web passes at once to a position of contact with the imprinting coating roll 5. In order to apply a controlled film of relatively dry coating material to the roll 5, we may employ a series of rolls 6, which rotate and some of which may oscillate endwise as well, after the style of any applying rollers in printing presses except, of course, that the roll 5 applies a complete coating on the web. The wet clay coating mixture to be imprinted is fed into gate rolls I. From the roll 5 the web passes through a dryer section having rolls 8, some of which are indicated in the diagram, and thence to a calender stack 9.for calendering the dried product.

Other mechanisms may be employed which are suitable for applying an imprinted coating on the web, drying it and calendering it.

Exemplary practices of producing uncolored, coated paper according to our invention vary in the manner used to associate the reactive resinous substance and its catalyst with the imprinted coating, the guiding rule being to do it in such manner that the imprinting characteristics of the wet coating mixture remain substantially unchanged.

In a preferred practice, we dissolve the catalyst in the water of the starch-clay coating mixture, apply the resinous substances to the paper surface of the web by means of the breaker stack of calenders and imprint the clay coating mixture over it.

In another practice we apply the resinous substance and its catalyst together on the breaker is dissolved in the clay coating mixture. the catalyst applied to the surface of the web by the breaker stack of calenders and the clay coating mixture imprinted over it. In this practice. the corrosive catalyst, e. g. ammonium chloride, can exert its effect on the hot metal calender rolls, which is undesirable. Similar but possibly less intense is the corrosive effect present in the second of our practices. We find, however, that this alternative practice of applying the catalyst in an under coat had advantages in confining the resinous substance largely to the coating as distinguished from placing it in direct contact with the fibrous surface.

As previously noted, the reactive resinous substance can be applied to the web on the breaker stack of calenders together with or separately from the application of the inert plastically smoothable surface treating agent. Thus, the reactive resin substance can be dissolved in the water solution which already contains the inert plasticizable smoothable surface treating agent and the combined solution applied to the web on the breaker stack of calenders. Alternatively, the reactive resin solution and solution of inert plasticizable smoothable surface treating agent can be applied separately to the surface of the web on the breaker stack of calenders. Similar arrangements are possible where the catalyst is applied to the web on the breaker stack of calenders and the reactive resin is intermixed in the wet clay coating mixture.

In a. test of the preferred practice, we mixed parts by weight of ammonium chloride catalyst into 85 parts by weight of regular clay coating with'starch adhesive and pigment, containing 54.0% solid, 46.0% water. The wet coating mixture so made had an acidic pH of 4.4. This coating mixture was used on the imprinting roll.

For use on the breaker stack of calenders to prepare the paper surface of the web for imprinting, we made a solution comprising equal parts by weight of urea formaldehyde resin syrup (70% resin solids to 30% water) and a solution of starch in water, the latter serving principally as the inert, plastically smoothable surfac treating agent. The latter comprised 6.75% converted starch of low viscosity, 93% water, and the remainder emulsified wax. Wax reduces stickiness of a solution in the calender nip. Thus, the composition of the solution used on the breaker stack of cala thickness of film on imprinting roll of the order 4 of about one thousandth of an inch, more or less.

Thence the coated web passed over drier section 8, which drier rolls were heated by 18 pounds of steam pressure and then on to and through finishing calenders 0. Actually in this test, the coated web also passed through a second stack of finishing calenders. not shown in the drawing. Finally, the calendered coated web was cut into sheets.

The coated surface of paperboard was then tested and found to be highly waterand rubproof. In one test, a black cloth moistened with water and with 500 grams weight thereon was applied to the coated surface and pulled across the sheet over a path 10 inches long, was lifted back to its original position, and the pull repeated. No clay coating was rubbed oil. onto the black cloth after 25 such 9 1118. whereas in the absence of our use of urea formaldehyde resin,

as described, coating rubs off onto the moist black cloth in one pull, and is completely removed from the web after a few of such pulls.

Another test applied to the coated surface of board was the well-known wet thumb test, whereby the thumb is moistened from one's tongue. placed against the coated surface of board supported by a table top and pressed hard as by weight of the body, being removed a moment afterwards, and the condition of the thumb noted. If the coated surface of board is water resistant and well bonded to the underlined paper, little or no clay coating will "come off" on the thumb. As applied to coated board made in the experiment just described, little or no coating adhered 1 to the thumb.

without the use of resin as described, results in enders comprised substantially 35% urea formaldehyde resin, 3.4% starch, .2% wax and 61.4% water by weight.

The resin we used in the test of our preferred practice was a syrup of urea formaldehyde resin, by weight in water and with weight ratio of 1.75 parts formaldehyde to 1.00 part urea, approximately. This resin is quite reactive and can be cold set by the addition of acid or acidogenic catalyst. Heat and time promote the cure. It is colorless and capable of being diluted with water to approximately 20% resin solids concentration before a permanent hydrophobe forms.

In erforming the test, the web of paperboard issuing from board machine dryer I was passed to breaker stack of calenders 3 where the starchresin solution-was applied to the paper surface by upper water box position I, which feeds solution into the nip of the corresponding calender rolls. From calender stack 3, the web passed at once to the position of contact with imprinting roll 5, where the mixture of regular clay-starch coating and ammonium chloride catalyst was imprinted over the resin treated surface of web, with complete removal of the clay coating from the paperboard surface.

A feature of clay coated board requiring control is the strength of coating and its adhesion to the paper surface. We find much improvement of these properties in coated board made by our process. Increases in wax Pick test of several numbers results from our process, as described.

Clay coated board with plain starch adhesive, printed with varnish base ink tends more readily to result in printing without gloss than otherwise. We find that marked improvement in gloss printing results from our process. Similarly, our product discolors less when treated with melted wax, as by momentary immersion.

In another practice we apply separately to the web on the breaker calender stack a water solution of the type noted in application Serial No. 501,320, now Patent 2,419,207. issued April 22, 1947, e. g., a solution of one volume of 5% polyvinyl alcohol to 4 volumes of 6% converted starch alone. Such a plasticizable solution is applied in upper water box I followed by a reactive resin solution comprising, e. g., 10 quarts water, 4 parts dry urea formaldehyde powder and .4 part of p, a 1 -ing with pram-scars: .adhesilefand' pigme t-com;

-ammoni um'chloflij del iiiikl l j bc 'lcr hisome other order. imprinting-"caster consistediof regularfcla y 1 Ex I a '5.-

- e4- 9361;: assassin 21 51amtam solids and} on :the fine printingroll was a'roumi one=thousandth ofan inch thick, more-a less.- Drierrolls foilowihg-the" imprinting-poster wereglieated' with 'la pounds? I mteamflprcs'sure, and 'th'e driedcoated board was -pa'ssed throughthe-flnishingcalender'.

pretreatment may be-entireiy of: polyvinyl alcohol with: many variations between, or the we stances of suitable excl-"us aboverefelrred 'io,fupto 12% of 1 yer-ted may be. used polyviny alto a plasticizahle surface,- or the .treatmentma-y comprise for other sub- 1 no Oui'pi'm has been describcd'interm of-i m.-

The productmade by thepractice just described exhibits marked improvement in water and rub resistance ofcoated surfacepompared .with the same coated board lacking the pretreat :ment with resin and catalyst. Further improve I lments continue as the coated sheet agesdn the pile. Application of additional heat to-the finished coated sheet, as by passage of it through a .heated tunnel, around another heated metal roll,

,and so forth, accelerates the aging and attain--;

mentof the maximum proofness commensurate with the quantity and quality of resin and catalyst used. However, in the practice just described, the clay coated surface is not so highly water and rub resistant as in the preferred practice although amply so for most uses; similarly,

1 it is less strong in pick test and the tendency to print with varnish base ink to a gloss finish is less pronounced. 1

In a variation of the practice just substitution for the 10 quarts of water may be -made with an equal volume of converted starch solution or of converted starch blended with polyvinyl alcohol in solution or of other suitable inert plasticizable surface treating agent.

the 10 quarts of water there may be substituted '10 quarts of solution. of 6% converted starch by weight; or 10 quarts of solution of starch and polyvinyl ancohol together. The starch and polyvinyl alcohol together may. comprise, but without- --limitation, one volume, of polyvinyl alcohol solu- -tion of 5% concentration by weight with 4 volumes of the 6% starch solution. In either instance, inclusion of inert plasticizable surface treating substance in the reactive resin solution ;makes it unnecessary to apply the former by separate water boxes on the breaker calender stack. 1

Starch-clay coated board not water resistant cannot be calendered in the presence of water on the finishing stack of calenders '9 because the starch of the coating dissolves in the water and .becomes sticky, whereupon the coating sticks to the metal calender rolls and the coated web plugs them necessitating a shut-down of the calender- --ing process. The water resistance of mineral coating obtained by our preferred practice is sufficient to permit the dried coated web to be calendered in the presence of water. Lesser degrees a of water resistance may still be sufl'lcietn to permit at least the moderate use of water or moisture on the finishing calender to enhance thesmoothness of finished mineral coated surface.

In the test of our preferred practice, the water resistant starch-clay coated surface calendered dry on finishing calenders 9 showing a Bekk smoothness value of 41 seconds.

Temperatures and amounts would naturally vary within wide limits, dependent upon the extent to which the imprinted coating is to be waterproofed, and with other types of initially water I soluble substances reacting in the presence of a catalyst with starch to insolubilize it.

The use of starch in ,the pretreatment is not required for the eifectto be gained. As set forth described Thus, I or breaker calender-stackspand so forth.-. We recognizthe-;ty of utilizing other mechanisms -withrour method of introducing waterprooflng'resinous or other substances into the coating, on paper or paperboard.

-We point out that there is latitude in the degrce of moistness of pretreating substance on the surface of the coated web when the mineral coating is imprinted thereon, to the extent that the pretreated surface of web is susceptible to water from imprinted mineral coating mixture.

- actant.

We obtain results in the described practice which we do not account for fully as a matter of theory. We do know that in addition to the absorption of resinous substance up into the mineral coating, that the paper surface of the web to which the coating is bonded also has been treated and made water and rub resistant with the resinous substance. llhis may account for the very high degree of water and rub resistance of the final product. This does not appear to be so much th case when the catalyst is applied first to the theretofore untreated web.

Our procedure, in preparing colored, coated paper is, by way of example, to mix into a normal starch-mineral coating mixture of standard materials, say, a white mixture rich in clay, a coloring' matter, water-soluble or water-dispersible, such as a soluble organic dyestuif or a dispersible pigment, lake, toner, etc., in finely divided condition, preferably in a little water, along with one of the insolubilizing reactants, the web already having been treated with another such re- I If a soluble dyestuff is added to the ratio of quantities of starch binder to mineral matter in the normal mixture will not be substantially disturbed; when pigments or lakes, etc.

are added, especially in large quantity to produce strong hues, it may be necessary to increase the content of starch in the normal mixture before adding the coloring materials, so that the proper ratio of starch binder to total mineral and coloring "matter will be maintained in the finished colored mixture. Otherwise, the starch binder present in the colored coating mixture applied to the paper surface may be insufiicient in quantity to properly hold the mineral matters and colors together and onto the paper surface and to give a coated surface of desired strength and quality. The standard Wax Pick test is a laboratory expedient for testing for proper amount of binder and with too little binder, even though insolubilized, a non-bleeding, non-smudging condition is not obtained,

Thus in an exemplary practice we prepare a normal starch clay coating mixture and conduct it to the coating machine. Close to the point of contact with this colored coating mixture it first has applied to its surface a dilute solution of a catalyst, such as here, but without limitation, ammonium chloride. Excess of catalyst is not critical; some of it is absorbed into the board surface. We may use one part or less ammonium chloride to three parts resin or even up to equal parts of catalyst to resin, all depending upon the particular dyestuif used, its concentration in the coating mixture and the absorbency of the paper surface of the board. Other catalysts found usable include ammonium oxalate, ammonium phosphate, ammonium sulphate, aluminum sulphate and tannic acid. Some of the same or other suitable dyestuff may be included in this treatment and, indeed, where the applied colored mineral coating is in thin layer, the additive coloring effect of dyestuif in this treatment becomes important.

When the colored mineral mixture is applied to the paper surface and the coated web-is dried and heated, e. g., fed over the heated drier rolls 8, the catalyst acts and the starch coating becomes insoluble. At the same time thedyestufl becomes "fixed in the coating and resists bleeding, rubbing off in the presence of moisture or upon exposure to water, etc. Complex reactions between dyestuff, resin and/or catalyst may result in the insolubilizing of the d'yestuff before the starch of the coating is insolubilized, as, for example, when resin and dyestufl are mixed together prior to being added to the normal coating mixture, although normally the heat is required to finish the fixing of the dyestuff and as well as the insolubilizing of the starch. Reference has been made to two examples of water- .soluble resins and this is not a limitation. This class of resin material behaves alike so far as insolubilizing starch is concerned when reacted with catalyst and all water-soluble dyes will precipitate insoluble chromophoric material while the starch itself will react to become insolubilized. These remarks are based on fairly extensive tests. Ureas and melamines are the most readily available resins for our purpose. Where a water-dispersible pigment, lake, or the like is used instead of a water-soluble dyestufi in the coating the same exemplary practice as above is followed. However, the reaction with resin and/or catalyst resulting in water-insolubility of coloring substance is absent completely or substantially in the coating since the pigment, lake, or etc. already is an insoluble substance.

The color process as described operates to perfection using the imprinting coating process described above and also in the patent there referred to. Thus the catalyst may be applied to the traveling web along with a plasticizable water-borne substance, such as five percent starch solution, or polyvinyl alcohol and starch solutions mixed together in desired proportions, for example one part by volume of five percent polyvinyl alcohol solution with four volumes of a six per- 10 cent converted starch solution (by weight). The web is then worked and smoothed, as between rolls. The use of a stack of breaker calender rolls 3, applying the solution on one roll and passing the web thereafter through a series of them, will result in working the plasticized surface of freshly-made paper board so that it will be smooth and have plasticity in subsequent steps of operation. The board with the worked and plastically-smoothed surface is then passed between printing rolls under pressure between them. In this operation a film of the colored mineral coating mixture, formed as above described, for example, is applied to the surface of one of the rolls in a uniform film which film is picked off by the web. To apply the film one practice is to apply the same to the one printing roll by means of applicator rolls 6 similar to those used in applying ink to the inking roll in printing presses.

In our above description of our process for producing uncolored, coated paper we have described the plasticizing operation, and the imprinting action, as is also true of the Fisher patent above referred to, and reference is hereby made to that disclosure.

In referring above to coloring matters we in- ,clude dyes, soluble earth colors, soluble mineral colors, pigments, lakes, toners, etc., further grouping them into water-soluble and water-dispersible classes with their well-known properties. These are handled similarly in the coating mixture and present the same problem. As a term to cover all types, we employ in the claims the term "water-sensitive" coloring matter meaning either water-dispersible, water-insoluble coloring 'matter such as pigments, lakes, toners, etc., or

water-soluble matter like dyes, earth colors, mineral colors, etc. The water-soluble substances dissolve to form a true solution while the waterdispersible colors like pigments, lakes, toners, etc., have been treated in manufacture to facilitate their dispersion in water as particles of micro scopic size but not in solution, the whole being handled like a dye in our coating mixtures.

Some organic dyestuffs do not become insolubilized and bound with the insolubilized starch as easilyas others in our process, requiring more insolubilizing agents to become non-bleeding and non-smudging in the colored coating. The waterdispersible coloring matters, being already insoluble in water, behave rather uniformly in the colored coating, chemical reaction between reactants and coloring matter being minor, if at all existent, and the insolubilizing reaction being concentrated on the starch binder of the coating.

Having selected the coloring substance to use to produce a desired hue of coating, laboratory control is readily applicable to determine its response to the insolubilizing and "fixing action of the resin and catalyst reactants used, and to determine the optimum ratios needed of reactants to starch, and starch to total quantity of coloring matters present in the coating mixture (including clays, pigments, lakes, toners, dyes, etc.).

There must be considered, too, the cumulative effect of color applied directly to the paper surface, as by the breaker stack of calenders just prior to the imprinting of colored coating mixture, where used to supplement the colored coating itself. In U. S. Patent No. 2,370,344, above referred to, it is disclosed that dye so applied to the paper' surface, not only stains that surface but also is absorbed into the mineral coating itself face obtained in applicants present process may be a color composite resulting from color of mineral coat itself, modified by absorption of color from underlying colored paper surface, and by show-thru of colored paper surface especially when the layer of colored mineral coating is very thin. In fact, adjustment and change of color of coating on board may be made rapidly, using a given colored mineral coating mixture, by merely changing the color applied directly by an initial step to the paper surface. Moreover, the initial coating itself may be colored by combinations of water-soluble dyes and water-dispersible, waterinsoluble coloring matter. That the behavior of organic dyestuffs in our process varies is understandable in view of their complexities of composition and properties. dyestuffs respond more easily to the insolubilizing and "fixing reaction in the mineral coating than do others; dyestuffs of the direct class, being relatively unstable acid colors, in general respond easily. We customarily employ dyestuffs of these classes in our process but do not restrict ourselves to their use. Soluble earth and soluble mineral to color it evenly. Hence, the colored coated sur- I Some acid and basic colors respond satisfactorily as to the su1- phur dyes. The finely-divided, water-dispersible, water-insoluble mineral colors, i. e. pigments, lakes, toners, etc., which have been treated to make them rapidly dispersible in water in particles of microscopic size, the whole behaving like a dye in the presence of water, also respond satisfactorily to the fixing" reaction of the insolubiiized starch binder of the colored coating.

As we explain it, the insolubilizing and fixing reaction in our colored coating used on a paper surface has several phases, including: insolubilizing of the starch and itsadhesive bond to the paper surface; the coincident binding together of the mineral and coloring matters and to the paper surface in an insoluble binder; the insolubilizing of organic dyes orother reactive coloring substances by their conversion into lakes through interaction between them and reactants i. e. the

, resin and/or catalyst), the lake being formed on nature of the coloring matter.

The amounts of coloring matter, resin and catalyst to use with mineral coating mixture in our process vary with nature of the coloring matter, shade of color desired, quality of bleedand smudge-resistance of dried coating desired. quality of starch binder in the coating mixture, quality of pretreatment of paper surface of web and its color, etc. These quantities following will guide laboratory control tests to establish proper amounts of ingredients to use with a given mineral coating mixture. For example, with a white coating mixture of some 50 percent solids content, comprising principally starch binder and clay, the remainder being water, the addition of water-soluble dyestuff equal in dry weight to one percent the weight of wet coating mixture pro- 12 ing; with 2V2\percent coloring substance a strong color results while progressively stronger and deeper colors result with further increases in quantity dye-stuff used. When pigments or lakes. etc. are used, being tinctorially weaker than dye-. stuffs, up to some 25 percent the weight of wet coating mixture may be required to give a strong color to the dried coating. Where the color of coating results from admixture of two or more different coloring substances, the total amount of color used will be as Just described. Particularly with the water-soluble dyestufl's, less is required to produce a given hue of insolubilized coating than with the same coating, not insolubilized. It is to be understood that these quantities of substances are exemplary only. With such colored 5 mixtures the reactive resin needed in admixture for complete or substantial water insolubility of dried coating and color may amount up to some 25 per cent or less the weight of wet colored coating mixture of some percent solids content, using a Water solution of polymerizable urea formaldehyde resin containing some percent solids by weight.

Catalyst and color added along with plasticizing substance when the paper surface of web is pretreated and prepared for the imposition of colored mineral coating mixture, as by imprinting, will be variable in amount. As a typical precoating solution we may employ converted or modified starch, ammonium chloride catalyst and dyestuif; the starch acts as plasticizable substance, the ammonium chloride catalyzes the insolubilizing and fixing reactions of resin with starch and coloring substances, and may react with coloring substance, too, and the dyestuff acts to stain the paper surface of web underlying "the later-imposed colored mineral coating and to stain and modify the color of mineral coating itself by absorption thereinto. A typical solution comprises:

3 Parts by weight starch solution Ammonium chloride catalyst 15 Dyestuff l-2 boxymethyl cellulose, etc. The dyestufl' in the starch solution preferably is of the acid group although basic and direct dyes may prove compatible with certain coloring substances in the starch-mineral coating mixture itself. The amount of dyestufl' used may be varied widely as needed to modify or bolster the color of the mineral coating itself. For example, without limitation, the 1-2 parts by weight of dyestuif in the solution may be increased to 25 parts, more or less, depending upon solubility of the dyestuff in the solution and the need for applying such a high concentration of dyestuif to the board surface.

A colored coating made by our process to possess insolubility of color and high resistance to wet rubbing must be tested todistinguish between them. Thus a dyestuif incorporated incur mineral coating mixture may have become insolubilized by the reactants and yet the colored coating may be removable from the coated surface of board by wet rubbing due to a deficiency in quantity of starch binder in the coating or insufflcient duces a tinted or moderately colored dried coat.- 7! water-resistance of the binder itself.

A convenient method of determining the water-insolubility or bleed-resistance of color in our colored coating employs a small hydraulic press and sheets of plain white blotting paper. One or more pieces of colored coated board to be tested are cut to a convenient size, say, tw inches One sheet of dry blotting paper convenient figure, say, 100 pounds per square inch Then the I maintained for one minute or so. pressure is released rapidly and the wet blotter stripped from the colored coatings. The color absorbed onto the wet blotter, properly examined after the blotter has been dried, gives a measure of insolubility of coloring matter developed through practice of our process. Ordinarily the colored coating itself will not stick to the wet blotter but if it does this may be an indication of insufficient bonding of coating to the board and must not be confused with the absorption of color due to water-solubility of coloring matter in the coating. Instances are known ,where the wet blotter has picked up color from coatings colored by water-insoluble coloring matter like pigments or lakes, being intrinsically insoluble, thus to show that insufficiency of quality or quantity of starch binder made water-resistant has been at fault, not the water-insolubility of the coloring substance. The effect of wet rubbing on our colored coating can be tested as described in connection with that facet of our invention which relates to the production of uncolored, coated paper, using a white instead of black cloth but otherwise proceeding as described, 1. e. moistening the cloth with water, applying it to the coated surface, placing a 500 gram weight thereon and pulling the weighted cloth across the sheet over a path several inches long, lifting the weighted cloth back to its original position and repeating the pull, as many times as deemed necessary. Where the proportions and quality of reactants, originallv-white coating mixture coloring substance, etc. have been adjusted to optimum conditions, resistance to wet rubbing may be so high that repeated pulls of the weighted cloth over the colored coated sheet will not remove enough coating to show up as colored stain thereon. However, resistance to wet rubbing of our insolubilized colored coating may suflice for given uses of our colored coated board when only a few pulls of the weighted wet cloth give traces of colored stain thereon, in comparison with a colored coating of similar nature, not insolubilized, which has no resistance at all to wet rubbing.

We have spoken above of using the catalyst in a preapplication step and the resin later in the mineral coating. This procedure can be reversed as set forth in connection with our basic process of producing uncolored, coated paper, and we also wish to include herein, with respect to the color aspects of our process, the various procedures of said basic process plus the use of water sensitive coloring matter.

Among the organic dyes which we have used 14 successfully are these following typical ones, grouped according to their constitution.

Commercial Name g g,

DYESTUFFS OF THE ACID GROUP Orange RR 161. Acid Green 20 Cone 670 Acid Blue B 736' Naphthol Yellow, Cone 10 ("rocelne Scarlet MOO 252 Tartrazine. 640 Azo Rubine B. 179 Nigrosine OPP. 865 Patent Blue 2Y Conn 712 Eosine J 768 DYESTUFFS OF THE BASIC GROUP l Safran'ine... 841 Malachite Green 667 Bismark Brown 332 Frmh inn 671 Methyl Violet H cs0 Chrysoidine l 20 Rhnrlnminp 74G Etc.

DYESTUFFS OF THEDIRECT GROUP Benzo Alllrine 502 Pontamine Black. 581 Ghrysonhenine 385 Bcnzo Blue Pontamine Blue. Congo Red...

Pontamine Fast Red 8BL.. Pontagtine Brown .L

A DYESTUFF OF THE SULPHUR GROUP Sulphur Black BB 986 1 Color Index of the Society of Dyers and Colourists," by Rowe, 1st edition, June 1924 and Supplement of 1928. v E

The water soluble mineral color, Soluble American Blue, being the ferro-cyanide of iron, and the water soluble earth color, Sap Brown, being the hardened extractive matter from decayed vegetation, also becomes insolubilized and ,.fixed in the coating of our process.

Among the pigments, made water-dispersible, are chrome yellow, green chromic oxide, red oxide of iron, carbon black, ultramarine blue, etc.,

v these being recognized commercially under well known trade names and varieties and being unassociated with organic dyestuffs.

The pigment dyes, so-called, we find usable in our process comprise lakes, toners, etc., formed in the well-known manners by precipitating dyestuff onto a finely-divided mineral base such as clay, alumina hydrate, or the like, or by precipitating out the organic substance itself as a highly colored substance, these being made into finelydivided forms easily dispersible in water. We use pigment dyes either in form of dry powders or as colored watery pastes. The commercial names and derivation of these substances form a compilation too complex to include herein. One skilled in the art will recognize them.

In the claims which follow we employ the terms reaction, reactive and reactant without attempting to explain the mechanism by which the starch becomes insolubilized.

Modifications may be made in our invention, without departing from the spirit of it. Having thus described our invention in exemplary embodiments, what we claim as novel and desire to secure by Letters Patent is:

1. In a process of treating paper webs which comprises passing a freshly made paper web through rolls and at the nip thereof applying thereto a plasticizing, film-forming, water-bourne substance chemicallyinert to the fibers, and then while retaining thedampened condition of the web surface, imprinting onto the web a coating comprising a mineral coating material and a starch binder in an aqueous vehicle, the steps of rendering the said coating resistant to wet rubbing by adding a thermosetting resin and a catalyst therefor to produce a reaction in which the starch of said coating is insolubilized, said process involving adding. not earlier than the application of said plasticizing substance, said resin and said catalyst, at least one of said last mentioned substances being imposed on the paper prior to the imposition of said coating.

2. The process claimed in claim 1 in which a coloring matter is applied to the paper web as an incident to one of the recited steps.

a. The process claimed in claim 1 in which said catalyst is added prior to the imposition of said coating and said resin is added with said coating.

4. The process claimed in claim 1 in which said catalyst is added prior to the imposition of said coating and said resin and a coloring matter are added with said coating.

5. The process claimed in claim 1 wherein said resin is added prior to the imposition of said coating and said catalyst is added with said coating.

6. The process claimed in claim 1 wherein said I resin is added prior to the imposition of said coating and said catalyst and a coloring matter are added with said coating.

7. The process claimed in claim 1 in which said resin and catalyst are added prior to the imposition of said coating. A

8. The process claimed in claim 1 in which said resin and catalyst are added prior to the imposition of said coating and a coloring matter is Number added with said coating.

9. Coated paperboard produced by the process of claim 1.

10. Coated paperboard produced by the process of claim 2.

11. Coated paperboard produced by the process of claim 3.

12. Coated paperboard produced by the process of claim 4.

13. Coated paperboard produced by the process of claim 5.

14. Coated paperboard produced by the process of claim 6.

15. Coated paperboard produced by the process of claim 7. Y

16. Coated paperboard produced by the process of claim 8.

l7. Coated paperboard produced by the process of claim 2 in which the coloring matter is a water soluble dye.

18. Coated'paperboard produced by the process of claim 2 in which the coloring matter is a water miscible pigment.

HARRY C. FISHER. BRAINARD E. SOOY.

REFERENCES CITED The following references are of record in the file of this patent:

. UNITED STATES PATENTS Number Name Date 313,799 Bancroft Mar. 10, 885 1,733,524 Bradner Oct. 29, 1929 1,982,018 Owen Nov. 27, 1934 2,123,152 Rivat July 5, 1938 2,130,530 Fletcher Sept. 20, 1938 2,185,746 I Goencz et al Jan. 2, 1940 2,256,853 Schwartz Sept. 23, 1941 2,322,887 Schwartz et a1. June 29, 1943 2,343,898 Griflin Mar. 14, 1944 2,370,344 Fisher Feb. 27, 1945 2,419,206 Fisher Apr. 22, 1947 2,419,207 Fisher Apr. 22, 1947 2,424,284 OIpin et al July 22, 1947 2,480,998 Nelson Feb. 8, 1949 FOREIGN PATENTS Country Date 559,329

Great Britain, Feb. 15, 1944 

1. IN A PROCESS OF TREATING PAPER WEBS WHICH COMPRISES PASSING A FRESHLY MADE PAPER WEB THROUGH ROLLS AND AT THE NIP THEREOF APPLYING THERETO A PLASTICIZING, FILM-FORMING, WATER-BOURNE SUBSTANCE CHEMICALLY INERT TO THE FIBERS, AND THEN WHILE RETAINING THE DAMPENED CONDITION OF THE WEB SURFACE, IMPRINTING ONTO THE WEB A COATING COMPRISING A MINERAL COATING MATERIAL AND A STARCH BINDER IN AN AQUEOUS VEHICLE, THE STEPS OF RENDERING THE SAID COATING RESISTANT TO WEB RUBBING BY ADDING A THERMOSETTING RESIN AND A CATALYST THEREOF TO PRODUCE A REACTION IN WHICH THE STARCH OF SAID COATING IS INSOLUBLIZED, SAID PROCESS INVOLVING ADDING, NOT EARLIER THAN THE APPLICATION OF SAID PLASTICIZING SUBSTANCE, SAID RESIN AND SAID CATALYST, AT LEAST ONE OF SAID LAST MENTIONED SUBSTANCES BEING IMPOSED ON THE PAPER PRIOR TO THE IMPOSITION OF SAID COATING. 